A comparison of the dose distributions between the brachytherapy 125I source models, STM1251 and Oncoseed 6711, in a geometry lacking radiation equilibrium scatter conditions

摘要

As the procedure has previously been detailed in [10], it is described briefly here. Dosimeters were irradiated with an 125I source ‘BARD STM1251' (Bard Inc., Murray Hill, NJ). The source was calibrated by the manufacturer with a stated air kerma strength of 0.317 U at the beginning of irradiation. The dosimeters used in this work were radiophotoluminescent glass rod dosimeters (GRDs) model GD-302M (Asahi Techno Glass Corporation, Shizuoka). The GRDs were calibrated in advance using a 6-MV X-ray beam from a linear accelerator (Primus KD2/7467, Toshiba Corporation, Tokyo). Calculations were carried out using the Monte Carlo (MC) code EGS5 [12]. The absorbed dose to the GRDs was calculated for the same geometry as the GRD measurement. The EGS5 output was then converted to an absorbed dose to water using the mass energy-absorption coefficient [11]. The calculation geometry included the 125I source, GRDs and the phantom placed on a Styrofoam block (25 × 25 × 20 cm thickness) and Pb (90 × 90 × 6 cm thickness). The geometry input for the 125I source (STM1251) was the same as that used by Kirov et al. [13]. The dose uncertainty for STM1251 was estimated in a manner similar to that of the Oncoseed 6711 investigation [7]. The dose uncertainties for each of the uncertainty components were combined in quadrature to obtain the Combined Standard Uncertainty (CSU) for the coverage factor k, set at 1.